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Plant-mineral nutrition: macro- and micro nutrients, uptake, functions, deficiency and toxicity symptoms


Academic year: 2023

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Luxury consumption consists of taking in more phosphate than is needed for growth and storing it inside the cell. The stored phosphorus is in the form of phosphate granules, or, for short periods, as RNA and ATP. This internal storage then allows a certain population growth even when the phosphorus reserves in the medium are depleted.

Most green plants need nitrogen in the form of nitrate ions (NO3-) and ammonium ions (NH4-). Although nitrogen in its gaseous state is abundant in the atmosphere, nitrogen in its gaseous state is unavailable to most life forms. Of the approximately 40 known species, the most common species in the genera Nostoc and Calothrix are found in both soil and aquatic habitats.

Nitrogen also becomes available through the breakdown of organic matter through ammonification, nitrification and denitrification, three other processes in the nitrogen cycle. Some of the ammonia is dissolved in water or absorbed by plants; another part is trapped in the soil and fixed in both acidic clay and certain basic saturated minerals. But from an agricultural point of view, denitrification is undesirable; it results in the loss of nitrogen from the soil and consequently a decrease in nutrients for plant growth.

The free-living non-symbiotic and symbiotic bacteria both require molybdenum as an activator and are inhibited by an accumulation of nitrates and ammonia in the soil.

Figure 2:  Important components of a generalized biogeochemical cycle
Figure 2: Important components of a generalized biogeochemical cycle

Carbon dioxide cycle

This reaction is carried out exclusively by prokaryotes (bacteria and related organisms), using an enzyme complex called nitrogenase. This enzyme consists of two proteins - an iron protein and a molybdenum-iron protein, as shown below. Then the reduced Fe protein binds ATP and reduces the molybdenum-iron protein, which donates electrons to N2 and produces HN=NH.

In two more cycles of this process (each requiring electrons donated by ferredoxin), HN=NH is reduced to H2N-NH2, and this is again reduced to 2NH3. Depending on the type of microorganism, the reduced ferredoxin, which supplies electrons for this process, is generated by photosynthesis, respiration or fermentation. There is a remarkable degree of functional conservation between the nitrogenase proteins of all nitrogen-fixing bacteria. The Fe protein and the Mo-Fe protein have been isolated from many of these bacteria, and nitrogen fixation can be shown to occur in cell-free systems in the laboratory when the Fe protein of one species is mixed with the Mo-Fe protein of another bacterium, although the species are very distantly related.

Carbon dioxide in atmosphere

Despite the small proportion of CO2 among the gases in the air, it is relatively abundant in natural waters. In natural dilute inland waters, CO2 in solution combines chemically with water molecules to form the weak carbonic acid.

Oxygen is one of the end products of this reaction, and it is released into the environment. The electrons removed from Hydrogen by water molecules are held by nicotinamide adenine trinucleotide phosphate (NADP) and NADP ic converted to NADPH. The synthesis of ATP molecules in chlorophyll by light energy is called "Photophosphorylation" (in the stroma of the chloroplast).

ATP molecules are universally present in living organisms and act as energy transfer compounds in biochemical reactions. ATP and NADPH molecules are used in photosynthesis to reduce CO2. For this synthesis, light energy is not required (dark reaction), and the reactions take place in the cytosol.

Light energy

Excited chlorophyll

The extent to which the system can withstand or adapt to disruptions of the existing equilibrium in the long term is of course uncertain. (Figure 13 and 14) Here comes the reference of humans and their role in biogeochemical cycles and the emission of anthropogenic pollutants (Figure 15).

Figure 12:  Carbon dioxide cycle
Figure 12: Carbon dioxide cycle


Nutrient/Mineral Significance

Plant uptake of trace elements (essential and non-essential)

Mucigel (grey) excreted by the root of the plant can facilitate or limit the uptake of elements. However, tissue accumulation will decrease due to dilution caused by increased biomass and because the rate of uptake is lower than the rate of biomass production. Movement of mineral elements on the root surface depends on i) Diffusion of elements along the concentration gradient formed due to uptake generating depletion of the element near the root. ii) Root disruption, where soil volume is displaced by root volume due to root growth. iii) Mass flow, the transport of bulk soil solution along the water potential gradient (transpiration driven) (Marschner 1995, Adriano (2001).

Mycorrhizae are known to increase the uptake of phosphorus by plant roots and prevent heavy metal and nitrogen-fixing bacteria help the plant to use atmospheric nitrogen (Marschner, 1995) (Figure 16). Elements that enter the cytoplast can also be moved to the vacuole via various mechanisms, depending on the element. This protects the micros from being bound by the potting media, making the micros more available to the plant.

Need for sophisticated analytical instrumentation for species-selective analysis of trace elements (micronutrients) in plants (Prasad 2004).

Figure 16:  Trace elements in soil solution  + Ligand =  related complex biogeochemical processes (rhizosphere  biogeotechnology)
Figure 16: Trace elements in soil solution + Ligand = related complex biogeochemical processes (rhizosphere biogeotechnology)

Need for sophistricated analytical instrumentation for species-selective analysis of trace elements (micronutrients) in plants (Prasad 2004)

Identification of metal-enzyme complexes and characterization of metal complexes with the products of enzyme-catalyzed reactions is an emerging area of ​​research in environmental speciation analysis. The success of using hyperaccumulating plants for phytoremediation of contaminated soils and waters requires a better understanding of the mechanisms of metal uptake, translocation and accumulation in plants. This was due to the lack of analytical techniques capable of providing information on the concentration of the multiple species in which each trace element is present in a sample.

The outer cell layer of the leaf surface consists of epidermis cells and on top of their cell walls a cuticle layer is formed containing cutin, pectin and cuticular lipids (also called wax). Copper is an essential component of the plant enzymes diamine oxidase, ascorbate oxidase, o-diphenol oxidase, cytochrome c oxidase, superoxide dismutase, plastocyanine oxidase and quinol oxidase. Like iron, copper is involved in redox reactions (Cu2++e-<=> Cu+) in the mitochondria and in the light reactions of photosynthesis.

This element is a component of the enzyme urease and is essential for its function (Gerendas et al. 1999). Many of the metalloenzymes are involved in the synthesis of DNA and RNA and protein synthesis and metabolism. Boron is one of the most essential elements for plant growth, which can be applied through soil or plant foliage.

Nevertheless, if the amount of the metal complexing ligand is limited (the case of soil solution ligands, which often have low affinity and low selectivity with respect to individual elements), or the ligand is very diluted, chelation may have no influence or may even improve a divalent cation uptake. Intact membranes are effective barriers to ions and uncharged molecules, but when solutes are more ... concentrated on one side of the membrane, they can diffuse down the concentration gradient using membrane carriers or even aqueous pores. Iron is required for the functioning of a number of enzymes, especially those involved in oxidation and reduction processes, for synthesis of the porphyrin ring (chlorophyll and heme biosynthesis), reduction of nitrite and sulfate, N2 fixation (as part of leghemoglobin) , etc.

Iron is a component of ferredoxin and participates in the composition of the thylakoid units, and therefore has important functions in electron transport as well as in photosynthesis (photosystem I). Therefore, iron homeostasis is regulated by complex mechanisms involving multiple pathways to reduce the toxic effects of the iron. The toxicity of the relatively unreactive superoxide radicals and H2O2 arises through the Fe-dependent conversion into the extremely reactive hydroxyl radicals (Haber-Weiss reaction) which causes severe damage to membranes, proteins and DNA.

Nutrient cycling in the ecosystem (unlike energy flow, which is unidirectional and a certain amount of energy is eventually dissipated). Leaf washing, precipitation, infiltration through soil, decomposition, uptake, transport of nutrients in and out of the ecosystem are linked to the hydrological cycle and cannot function without water.

Figure 19: Foliar uptake of trace element  Copper
Figure 19: Foliar uptake of trace element Copper


Some are temporarily bound in organic spaces, while some are trapped in deep sediments and rocks. Hydrologic cycles connect the terrestrial and aquatic ecosystem, thereby relating the local ecosystem to the global ecosystem. Ionomi” is an important and broad biological phenomenon, including electrophysiology, signaling, enzymology, osmoregulation and transport.

Understanding "ionomics" and its interaction with other cellular systems such as the genome, proteome, metabolome and environment is integral to our complete understanding of how plants integrate their organic and inorganic metabolisms. Non-metallic nutrients such as phosphorus, sulfur or nitrogen form the "ionome", while metals such as zinc, copper, manganese and iron form the "metabolome".

Figure 24: “Ionomics” is an important and broad biological phenomena, including electrophysiology,  signaling, enzymology, osmoregulation and transport
Figure 24: “Ionomics” is an important and broad biological phenomena, including electrophysiology, signaling, enzymology, osmoregulation and transport


Figure 1:  Generalized model of an ecosystem showing interaction between nutrient pool and biotic  compartment
Figure 2:  Important components of a generalized biogeochemical cycle
Figure  3:  Big bang theory and origin of elements of nutritional significance
Figure 5:  Schematic representation of sulphur cycle


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Abbreviations CFD Computational Fluid Dynamics FDM Finite Difference Method FVM Finite Volume Method ODE Ordinary Differential Equation PDE Partial Differential Equation FEM Finite